Grandma's Famous Sheet Cake

This cake recipe, Grandma's Famous Sheet Cake, leans on cornstarch, fresh lemon juice and clear or regular vanilla extract. It makes 20 to 20 servings and takes about 205 minutes.

• Yield 20 to 20 servings
• Ready in 205 minutes
• Prep 60 minutes
• Cook 25 minutes

Ingredients

Fruit Topping

• 2 ½ cups ( 365 g, more or less ) fresh or frozen fruit, like blueberries, raspberries, blackberries, huckleberries, triple berry blend, etc
• ¾ cup ( 177 g ) cold water (use 2 to 3 extra tablespoons water if using fresh fruit)
• ⅓ cup ( 71 g ) granulated sugar
• 2 ½ tablespoons cornstarch
• 1 tablespoon fresh lemon juice

Cake

• ½ cup ( 113 g ) salted butter, softened to room temperature
• 1 ⅓ cup ( 283 g ) granulated sugar
• ⅓ cup ( 65 g ) vegetable oil (or other neutral flavored oil)
• 4 large ( 120 g ) egg whites, room temperature
• 1 teaspoon clear or regular vanilla extract
• 1 ¾ cups ( 249 g ) all-purpose flour
• 1 tablespoon baking powder
• ½ teaspoon salt
• 1 cup ( 242 g ) 2% or whole milk, room temperature
• ¼ cup ( 56 g ) full fat sour cream, room temperature

Cream Layer

• 6 ounces ( 170 g ) cream cheese, softened to room temperature
• ½ cup ( 57 g ) powdered sugar
• 1 tablespoon fresh lemon juice
• ½ teaspoon vanilla extract
• 2 cups ( 480 g ) chilled heavy whipping cream

Instructions

1. For the fruit topping, in a medium saucepan, combine the fruit, cold water, sugar cornstarch, and lemon juice. Stir to combine until the cornstarch is dissolved.
2. Cook over medium heat, stirring often, until the mixture begins to simmer. Continue to cook, stirring constantly, until large bubbles pop at the surface and the mixture has thickened (it will thicken a bit more as it cools).
3. Scrape the mixture into a container with a lid. Cover, and let cool completely. The fruit topping can be made several days in advance and refrigerated.
4. For the cake, preheat oven to 350 degrees F. Position a rack in the middle of the oven. Lightly grease a half sheet pan (about 17X12-inches) with nonstick cooking spray and set aside.
5. In the bowl of a stand mixer fitted with the paddle attachment or in a mixing bowl with a handheld mixer, add the butter, sugar and oil. Mix on low speed until combined. Increase mixer to medium speed and mix for three full minutes, scraping down the sides of the bowl as needed, until the mixture is very light in color. Don't short this step - it's important for a moist, tender cake.
6. Add the room temperature egg white and vanilla and mix until evenly combined.
7. In a separate bowl, whisk together the flour, baking powder and salt.
8. Measure the milk into a liquid measuring cup and add the sour cream. Whisk to combine.
9. Add 1/3 of the flour mixture to the cake batter. Mix on low speed until just combined (a few dry streaks of flour are ok). Add 1/2 of the milk mixture and mix until combined. Add 1/3 of the flour. Mix. Add remaining milk mixture. Mix. Add final addition of flour and mix until just combined and no dry streaks remain.
10. Spread batter evenly in the prepared pan. Bake for 20 to 22 minutes until the center of the cake springs back lightly to the touch. Don't over bake.
11. Remove from the oven and let the cake cool completely in the pan.
12. For the cream layer, in the bowl of a stand mixer fitted with the paddle or whisk attachment or in a mixing bowl with a handheld electric mixer, mix the cream cheese and powdered sugar together until smooth and creamy.
13. Add the vanilla and lemon juice and mix until combined.
14. Add 1 cup heavy cream. Mix until combined. Add remaining heavy cream and mix on low speed until combined. Increase speed to medium and continue mixing until the mixture has thickened to soft peaks. It should be thick, creamy, but still very spreadable (don't over mix).
15. To assemble, spread the cream topping evenly over the cooled cake. Refrigerate the cake for about an hour for the cream layer to firm up a bit (you can skip this step, but it may make the fruit topping harder to spread without swirling the cream layer).
16. Dollop the fruit topping in large spoonfuls across the cream layer. Spread evenly across the cake.
17. Serve immediately or chill the cake for up to 2 hours before serving (any longer and the fruit topping may discolor the cream layer a bit - still tastes great).

Cool the layers before you stack them.